The present invention relates to a water pumping system for a pit such as a well or a borehole containing water at its bottom which has to be pumped to the surface of the pit. The system includes a feeding unit to be installed above the ground which surrounds the pit, and a suction ram assembly to be immerged into the water in the pit. The suction ram assembly comprises a ram valve and a foot valve. A riser pipe which is concentrically placed in a feed hose connects the surface feeding unit with the underwater suction ram assembly.
A water pumping system of that concentrical kind is known from German Patent No. 804,288. As is well known with such suction ram assemblies the ram valve shows a shut-off threshold force which in the pumping system of the above-mention German patent is determined by the poppet weight of the ram valve.
That system and similar systems cannot secure a fail-safe operation for several reasons. The intricate physical laws governing an automatic operation of a suction ram impose amongst other conditions an adjustment of the valve shut-off threshold dependent on various working parameters and a surge-free feeding pressure, if a correct self-alternance of the opening periods of the ram valve and the foot valve has to be maintained under severe conditions including polluted sump water, air inclusions and feed irregularities. Pumping devices to be installed at the bottom of a pit are of no practical use, if their self-oscillating operation is subject to failures or if they have to be lifted out of the pit whenever the poppet of the ram valve should become clogged. Moreover known pumping systems do not comprise any means for efficiently starting or restarting the suction ram assembly from the surface ground of the pit nor for adjusting the shut-off threshold force of the ram valve or for performing a gas cushion control from the surface ground.